Fix: Meetme recording variables from realtime DB use null entries over channel variables

Meetme would attempt to substitute the realtime values of RECORDING_FILE and
RECORDING_FORMAT from the meetme db entry instead of using the channel variable set
for those variables in spite of those database entries being NULL or even lacking
a column to represent them.

(closes issue ASTERISK-18873)
Reported by: Byron Clark
Patches:
	ASTERISK-18873-1.patch uploaded by Byron Clark (license 6157)
........

Merged revisions 347369 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@347383 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_meetme.c

@@ -4014,8 +4014,12 @@ static struct ast_conference *find_conf_realtime(struct ast_channel *chan, char
 			cnf->useropts = ast_strdup(useropts);
 			cnf->adminopts = ast_strdup(adminopts);
 			cnf->bookid = ast_strdup(bookid);
-			cnf->recordingfilename = ast_strdup(recordingfilename);
-			cnf->recordingformat = ast_strdup(recordingformat);
+			if (!ast_strlen_zero(recordingfilename)) {
+				cnf->recordingfilename = ast_strdup(recordingfilename);
+			}
+			if (!ast_strlen_zero(recordingformat)) {
+				cnf->recordingformat = ast_strdup(recordingformat);
+			}
 
 			/* Parse the other options into confflags -- need to do this in two
 			 * steps, because the parse_options routine zeroes the buffer. */